The herein disclosed invention finds applicability in the field of water purification and in the field of toxic waste removal; and specifically where residues of chlorite are found in aqueous solutions.
There is a need in the field of water purification to remove chlorite ion from water prior to use or disposing of the water in order to make the water non-toxic. No good way of destroying chlorite ion has been found, until now. Methods have been found, which require pH adjustment, produce sludge, or have some other drawback. Ascorbic acid reaction with chlorite is pH independent from 2.5 to 8.2, probably higher, and destruction of chlorite is virtually instantaneous.
Chlorite is toxic to several invertebrates which are important in the food chain. Chlorine dioxide (ClO2) in disinfection and other applications results in chlorite ion in the water. When this water flows to a receiving stream or other body of water, chlorite must be reduced to very low levels to meet governnent regulations.
Chlorite removal is difficult. Known chlorite removal chemistries are slow, produce sludge, require precise pH control or produce unwanted by-products.
Current regulations in some locations require chlorite ion to be at or below 0.006 ppm in water entering receiving streams; in other locations the amount of chlorite entering the stream may be higher. When chlorine dioxide (ClO2) is used at normal usage levels, typically 0.5-1.0 ppm above demand (which can be higher with 2.0 ppm being typical), a total of 2.5-3.0 ppm ClO2 is used. Approximately 50-80% of this ClO2 is converted to chlorite ion. If 3.0 ppm is fed, 1.5-2.4 ppm of chlorite ion can be produced. This amount varies depending upon water conditions. Under certain conditions, depending on the contents of the water, less chlorite will be produced. Therefore, to use ClO2 for a given application, any reducing chemistry for chlorite destruction must be able to reduce chlorite to chloride ion or some other innocuous species. Since most of these systems are once-through, the water velocity is such that any treatment must act quickly and completely to reduce chlorite before discharge. Therefore, any treatment must reduce chlorite levels to essentially immeasurable levels of innocuous species in a few seconds. The treatment itself must also be innocuous, in the event of over treatment.
European Patent 0 196 075
European Patent 0 196 075 describes the preparation of a contact lens cleaning solution wherein ascorbic acid is added to chlorite to accelerate the decomposition of chlorite. In decomposing the chlorite by the use of acid, chlorine dioxide is produced. On page 2 the patent identifies the system as containing a chlorite salt in aqueous solution and an agent for accelerating the decomposition of chlorite. The accelerating agent can be an acid. And on page 5, next to the last line, ascorbic acid is listed as the acid accelerating agent. Note also claim 1, taken with claim 5, identify the agent for accelerating the decomposition of chlorite to form free oxygen as ascorbic acid. The inventive concept of the herein disclosed invention is distinct from that of European patent 0 196 075. The herein disclosed invention employs adequate ascorbic acid to completely inactive the chlorite ion and to convert it to chloride. The European patent does not.
Further note that European 0 196 075, page 19, Table 3, discloses adding 0.01 g of ascorbic acid to a 0.06 g solution of sodium chlorite. These amounts are opposite those used in this invention. The herein disclosed invention for example uses approximately five parts ascorbic acid to destroy one part chlorite.
The formulation of 0 196 075 is designed to release free oxygen from chlorite. Two components are needed. They are (A) an aqueous solution chlorite, and (B) another solid component containing, (i) an agent for accelerating the decomposition of the chlorite to form free oxygen, selected from acids, organic acid salts, ion exchange resins, reducing agents and sugars, and (ii) an agent for consuming excess free oxygen from the decomposition of the chlorite after impurities have been removed.
The patent refers xe2x80x98forming free oxygenxe2x80x99 appears to actually refer to the formation of ClO2. This is the reason acids, organic acid salts, ion exchange resins and sugars are used.
On page 5, paragraph 4, the patent states:
xe2x80x9cThese agents (acids, organic acid salts, ion exchange resins, reducing agents, and sugars) act as a catalyst for accelerating the decomposition of the chlorite contained in the component A. The agents may function by releasing hydrogen ion, which leads to accelerated decomposition of the chlorite to form free oxygen.xe2x80x9d
In paragraph 6 of the same page, they state,
xe2x80x9cThe acid may be any one as long as it provides the function required in the present invention. Preferred examples of the acids include organic acids such as adipic, stearic, sebacic, oxalic, itaconic, edetic, ascorbic; and inorganic acids such as hydrochloric and sulfuric acids. It is more preferred to use tartaric and/or citric acid . . . .xe2x80x9d
The inclusion of mineral acids and citric as the preferred embodiment indicates that it is indeed the formation of chlorine dioxide from chlorite that is being referred to here. Just as found in many other patents, when the inventors find an organic acid that appears to be operative, they include other organic acids.
Further in the text, on page 19, in Table 3, a series of products that include chlorite activated by various organic acids. This indicates that the European patent considered ascorbic acid to be just another organic acid. It does not appear that ascorbic acid was recognized as having special properties and considered to be a distinct acid, unlike other organic acids in its effect.
Based on a review of this patent, it appears that what the authors refer to as decomposition of chlorite to form free oxygen is actually activating chlorite to form ClO2. There simply is no recognition in European 0 196 075 of the special reactive nature of ascorbic acid with chlorite to form chloride.
On the other hand, the herein disclosed invention requires substantial amounts of ascorbic acid to destroy the chlorite ion and convert it to chloride. Amounts which are beyond the parameters of the European patent, note as follows: The herein disclosed invention employs approximately 5 ppm ascorbic acid to consume 1 ppm of chlorite ion. This ratio of components is distinct and just the opposite of that of European 0 196 075 which in Table 3, page 19, uses 0.02xc3x973=0.06 g of sodium chlorite with 0.01 g of ascorbic acid. It takes about approximately 5 ppm of ascorbic acid to consume 1 ppm of chlorite ion. The reaction is immediate, pH independent, and results in the formation of the chloride ion. No chlorine dioxide is formed as long as ascorbic acid is in a slight excess.
So far as the Opflow, American Water Works Association Vol. 24, No. 12, December 1998, pages 1, 4 and 5 publication is concerned, the reference does not speak of deactivating chlorite. The reference speaks only of reducing chlorine or inactivating xe2x80x9cchlorine levelxe2x80x9d. This is distinct from reducing chlorite levels. Nor are the herein disclosed critical proportions of reactants set forth.
European 0 207 633 does disclose both chlorite and ascorbic acid, however, this disclosure is so broad as to not read on your discovery.
Less pertinent references are noted:
Griese, et alxe2x80x94Chemical Abstracts Vol. 115:166,2229 discloses the use of sodium thiosulfate and sulfites to eliminate chlorine dioxide and chlorite ions, residuals, from drinking water.
May U.S. Pat. No. 4,851,130 teaches the use of erythorbate and ascorbate for oxygen removal.
Reynolds in U.S. Pat. No. 4,609,472 teaches the removal of chlorate ions from brine using acid and hydrazine hydrochloride.
Chvapil et al in U.S. Pat. No. 5,104,660 teach an antimicrobial wound dressing which may comprise sodium chlorite and ascorbic acid along with many other components. There is no suggestion in this reference to use ascorbic acid to rid the chlorite ion from an aqueous solution.
European Patent 0 315 185 teaches methods of polymerization in which chlorite and ascorbic acid may be reactants.
Tell et al in European 0 107 633 teaches sterilizing compositions in which ascorbic acid and chlorite may be reactants, however, this reference does not teach the inventive proportion of ingredients or method of use as disclosed herein.
Peterkaxe2x80x94Opflow Vol. 24 No. 12, December 1998, pages 1, 4 and 5 teaches ascorbic acid to neutralize chlorine in water. The reference does not teach chlorite in solution or the use of ascorbic acid to destroy chlorite.
Review of Existing Chlorite Reduction Methodologies
Granular Activated Carbon and Reverse Osmosis: Although partial or complete removal of chlorite is possible with these technologies, none of these technologies are practical for large industrial facilities when the throughput is on the orders of 100,000 gallons per minute.
Sulfur Dioxide and Sulfite Ion: SO2 and SO32xe2x88x92 have been shown to remove ClO2xe2x88x92 by Gordon.1 In the pH range 4.0 to 7.5, the reaction is shown below:
2SO32xe2x88x92+ClO2xe2x88x92 greater than 2SO42xe2x88x92+Clxe2x88x92
1 Gordon, G., Slootmaekers, B., Tachiyashiki, S., and Wood, D., xe2x80x9cMinimizing Chlorite Ion and Chlorate Ion in Water Treated with Chlorine Dioxide,xe2x80x9d Journ. AWWA, page 160, April 1990. 
In the presence of oxygen and at elevated pHs, the reaction chemistry deviated from the equation shown above.
Dixon et al and Griese et al2,3 observed that the presence of oxygen in the reduction of chlorite with SO2 or SO32xe2x88x92 resulted in the formation of chlorate. They suggested that the use of sulfur-based reducing agents for removal of chlorite in potable water was not a viable option.
2 Dixon, K. L., and Lee, R. G., The Effect of Sulfur-Based Reducing Agents and GAC Filtration on Chlorine Dioxide By Products, J. AWWA, May 1991, page 48. 
3 Griese, M. H., Hauser, K., Berkemeier, M., and Gordon, G., xe2x80x9cUsing Reducting Agents to Eliminate Chlorine Dioxide and Chlorite Ion Residuals in Drinking Water,xe2x80x9d J. AWWA, May 1991, page 56. 
The reaction of chlorite with SO2 and SO32xe2x88x92 is complete in less that a minute below a pH of about 5.0.
However, for large industrial once-through applications, where 100,000 gpm through-put is common, it is not feasible nor environmentally acceptable in many cases to add sufficient acid to depress the pH of the water to  less than 5.0 to get rapid chlorite destruction.
Ferrous Iron: Chlorite ion can be reduced to Clxe2x88x92 by ferrous iron (Fe2+), as shown in the following equation.
4Fe2xe2x88x92+ClO2xe2x88x92+10H2O less than  greater than 4Fe(OH)3(s)+Clxe2x88x92=8H+
In this reaction, chlorite ion is reduced to chloride ion, and the iron forms a ferric hydroxide floculent which ultimately settles (s) out in the water.
Ondruss et al4 investigated the kinetics and found that at pH  less than 2.0 and high ionic strength condition (2.00 M), the reaction proceeded at a rate that would be acceptable for potable water plants.
4 Ondruss, M., and Gordon, G., xe2x80x9cThe Oxidation of Hexaaquoiron (II) by Chlorine (III) in Aqueous Solution,xe2x80x9d Inorg. Chem., 11(5), 985(1972). 
Ferrous iron (Fe2+) has been used with good results by several potable water facilities.5 
5 Tarquin, A., Hansel, G., Rittmann, D., xe2x80x9cReduction of Chlorite Concentrations in Potable Water with Ferrous Chloride,xe2x80x9d Water Engineering and Management, 35 (February, 1995). 
The use of ferrous iron may be acceptable for potable water facilities, because they have the capability of handling the sludge produced. In addition, their holding time permits a somewhat slower reaction to proceed. However, for large industrial once-through facilities, ferrous iron is much too slow and the sludge produced is generally environmentally unacceptable.
1. Ozawa, T., and Kwan, T., xe2x80x9cDetoxification of chlorine dioxide (ClO2) by Ascorbic Acid in Aqueous Solutions: ESR Studies,xe2x80x9d Wat. Res 21 (2), 229 (1987) describes problems with ClO2 in potable water. The addition of ascorbic acid to a solution of ClO2 is proposed to produce the following:
ClO2+AsA greater than ClO2xe2x88x92+AFR
AFR greater than AsA+DasA
where AsA=ascorbic acid, AFRxe2x80x94ascorbic acid free radical, and DasA=dehydroascorbic acid.
No mention is made in this article of ascorbic acid reacting with chlorite.
2. Collings, G., Yokoyama, M., and Bergen, W., xe2x80x9cLignin as Determined by Oxidation with Sodium Chlorite and a Comparison with Permanganate Lignin,xe2x80x9d J. Dairy Sci, 61(8), 1156(1978). Sodium chlorite oxidation is a technique of plant research for 30 years, involves taking some plant residue and adding acidified chlorite to the sample. The oxidation reaction is stopped by adding ascorbic acid. However, no mention of chemistry of exactly what is stopped. The implication is that chlorine dioxide oxidation is what is causing lignin removal, and ascorbic acid stops that reaction.
In summary, for large industrial facilities, no good, rapid, environmentally friendly method for reducing chlorite ion has been found.
None of the prior art teaches the use of ascorbic acid in amounts which will convert chlorite in solution to chloride ion.
An object of this invention is to reduce chlorite in aqueous solution to chloride.
A further object of this invention is to reduce chlorite in solution safely and rapidly.
A major object of this invention is to produce a method which will reduce chlorite in a manner which is innocuous.
The inventor has found that ascorbate ion or its isomers react with chlorite in an unexpected manner. The invention herein disclosed is unique in recognizing that a specific amount of ascorbic acid is required to convert the chlorite ion, not to chlorous acid (HClO2) which disassociates to form chlorine dioxide (ClO2) but to chloride ion (Clxe2x88x92) which is innocuous in the receiving stream. For example, if the pH of an aqueous solution of chlorite ion is lowered to less than pH 7, by addition of acid, whether organic or inorganic, chlorite ion forms chlorous acid, HClO2, which then dissociates to form chlorine dioxide, ClO2. The rate of reaction is a function of pH, the lower the pH, the more rapid the reaction. From the work of the inventor, it is clear that every acid (e.g., the ones that would dissolve in water) depressed the pH to a greater or lesser extent. The rate at which ClO2 formed was a function of the final pH.
Ascorbic acid, if used at less than about a ratio of 2 moles ascorbic acid to 1 mole chlorite ion, would end up forming ClO2, because of the pH depression. If sufficient ascorbic acid is used, no ClO2 is formed. The chlorite ion reacts with ascorbic acid to form chloride ion. This reaction chemistry is novel and unexpected. The a preferred ratio of ascorbic acid to chlorite would be about 5.2 ppm ascorbic acid to 1 ppm of chlorite.
The inventor observes that when chlorine dioxide is applied to a solution which is to be disinfected, that after the chlorine dioxide does its disinfecting, about 70%-90% of the time, chlorine dioxide reverts back to chlorite ion. The chlorite ion is not decomposed, but is activated to chlorine dioxide, which, after disinfecting, ends up as chlorite ion. The chlorite ion is still in solution. When ascorbic acid is added to chlorite ion at the correct molar ratio, ascorbic acid xe2x80x98reducesxe2x80x99 the chlorite ion to chloride ion, which is innocuous in potable water.
Chlorite ion is a problem in numerous applications, not the least of which is potable water disinfection.
In many instances throughout the specification, approximate ratios or amounts of ascorbic acid to destroy chlorite have been set forth. Tests done in the laboratory have defined the stoichiometry of chlorite destruction by ascorbic/erythorbic acids. The reaction requires approximately 2 moles of ascorbic (or its isomer erythorbic) acid per mole of chlorite ion. In terms of ppm, it takes about 5.2 ppm ascorbic acid (or erythorbic acid) to destroy 1 ppm of chlorite ion.